There are federal rules about this. If you are in school more than half-time and don't have kids or a disability then you have to have a work-study award and work at least 20 hours/week for food stamps and TANF, OR the school has to be a community college and in a program that leads directly to employment.

When you fill out the FAFSA, parental information is optional for grad students but if you don't submit it or if submitting it reveals middle class parents, the school isn't going to give you one of its work-study vouchers, which are in limited supply.

It's a roundabout way of doing it, but the feds are aware of the abuse potential and have taken steps to ensure that the fake "independence" that is automatically granted to graduate students doesn't get used to get SNAP and TANF. So yeah, if you are genuinely poor you might be able to get it, but the "fake poor" of a graduate student with no responsibilities living off student loans isn't gonna cut it. Basically, if the school doesn't see you as poor enough for work study then TANF and SNAP won't see you are poor enough for welfare.

That said, if you are in a state that has expanded Medicaid under the ACA, students may be able to qualify for that, though most don't even think about it because their parents can now keep 'em on their plan to age 26, or the school will passively enroll you in their own insurance and give you more loans to pay for it.